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| Fig. 1: Diagram of carbon capture from the atmosphere. (Source: D. Kuldinow) |
It is said that necessity is the mother of invention. Climate change is such an enormous existential threat that a number of industries are coming into being to fight against it. In the past decade, the markets for electric vehicles, solar panels, and sustainable food programs have ballooned in size.
However, the most ambitious venture is arguably Carbon Capture and Storage (CCS). This technology removes carbon dioxide from the environment directly and stores it somewhere it will not have an adverse effect. As shown in Fig. 1, typically, air (exhaust or ambient) is passed through some filter which reacts with the CO2 and removes it from the flow. Obviously, for this to have any meaningful effect, the CCS technologies will need to extract an amount of carbon within an order of magnitude of the global production of carbon.
For the purposes of this analysis we shall consider two CCS methods: (1) power plant post-combustion capture and (2) direct air capture.
In post-combustion capture, one feeds the exhaust of a power station through a series of reacting tanks - which then react with the carbon dioxide to either sequester the CO2 in an inert compound or to concentrate it and release what remains. These methods have the ability to reduce the emissions of a plant by 80-90%, but come at enormous cost. [1] One study estimated that constructing and maintaining the CCS system for a medium-sized 400 MW power station that captures 90% of its exhaust CO2 would cost about $1 Billion over the course of 5 years, and would increase the cost of the electricity by 50%. [1-3] Given the nearly 2500 fossil-fuel burning power plants in the U.S. alone, to achieve meaningful change would require a multi-trillion dollar investment. [4] Even so, the current implementation of these systems are not flawless, and full-scale CCS power plants are scarce. At one such plant in Canada, SaskPower, reports showed that the carbon capture project had serious design issues and was only operational about 40% of the time. [5] Thus, even if the current state of the art post-combustion carbon capture systems were installed at great expense at every power plant in the world, it may only reduce emissions by 40%, which is significant in this sector, but clearly an absolute maximum.
The majority of emissions, however, do not come directly from power plants. A far greater fraction comes from a sum of transportation, commercial/residential (heating homes etc.), and agriculture. This emission takes place on a small, non-centralized scale, so we do not have the benefit of being able to install infrastructure around the exhaust.
Thus, Direct Air Capture (DAC) was posited as a way of extracting CO2 directly from the atmosphere. It typically involves a reactant like Potassium Hydroxide, which then reacts with the CO2 to form Carbonates. These can then be further transformed into into inert precipitates. Currently, the world produces about 40 Gigatons (Gt) of CO2 per year. Climeworks, a leading company in DAC technologies constructs modular devices which each absorb about 500 t CO2 per year, on about 212 m2 of footprint and require about 91.3 kW to operate. [6] In total, they estimate that the total power requirement to blow the air through the reactors and sequester 106 t CO2 per year would be about a continuous 300 MW, which, optimistically, could cost in total as little as $100 per ton. [6] Scaling this up to absorb even 10% of global emissions would require
| Total Power Requirement | = | 10% × (Emissions) × (Power required per ton CO2) | |||
| = |
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| × (300 W y t-1 × 365 d y-1 × 24 h d-1 3600 sec h-1) | |||||
| = | 12 × 1011 Watts = 1200 GW | ||||
| Total Land Area Requirement | = |
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| = |
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| = | 1.70 × 109 m2 = 1700 km2 | ||||
| Total Cost | = | 10% × (Emissions per year) × (Cost per ton) | |||
| = | 0.1 × 40 × 109 t y-1 × $100 t-1 | ||||
| = | $4.0 × 1011 y-1 = $400 billion y-1 | ||||
Since we are dealing with a cleanup on a humanity-wide scale, these numbers are likewise on such a scale. The electric power requirement to capture only 10% of the global carbon output is greater than the power consumption of all of America and Europe combined; sequestering all of the CO2 would require 10 times this estimate, approaching the scale of total global power consumption. [7] Currently much of the energy for Climeworks comes from geothermal sources, so is in some sense "free," but not scalable up to the required size: a footprint of about 30 times the size of Manhattan island, with and upkeep of $4 trillion per decade, even making the big assumption that Climeworks meet all of their efficiency goals moving forward. Clearly, this would also be an enormous, continuous investment and would take decades to build.
But also, it would simply not be technologically feasible without enormous strides in renewable energy as well. Currently less than 15% of total energy production, renewables would need to be the vast majority of production, with a significant amount going to carbon capture for the emitting proportion of energy production to break even. Since it clearly makes no sense to be emitting as much carbon as you're absorbing, CCS can't be a significant, viable method for reducing climate change until it can be deployed en masse and powered entirely from renewable energy.
Finally, Climeworks disposes of the removed carbon by injecting carbonated water into porous rocks, which reabsorb the gas into carbonate rocks. On a global scale, any single reservoir of carbonates would quickly saturate. Thus there would be additional costs and considerations associated with how to dispose of the remaining carbon.
The promise of Carbon Capture technologies can certainly be one part of a comprehensive greenhouse-gas emission reduction plan. However, it is clear that current technologies are not sufficient, on their own, to make a significant dent in the worlds emissions without enormous investment for the construction, land, and also higher prices for the consumer. Thus, at this time, there can really be no merit in speaking of carbon offsets and continuing to emit at the same rate, hoping that capture technologies will catch up. However, even so, thinking optimistically, there will come a time when emissions have been lowered to a rate within range of CCS; by this time, however, the climate will most likely have warmed significantly, and catastrophic climate events will be more common. Then, CCS technologies, along with re-forestation, will be required to reverse the effects of climate change.
© Derek Kuldinow. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] T. Wilberforce et al., "Progress in Carbon Capture Technologies," Sci. Total Environ. 761, 143203 (2021).
[2] E. S. Rubin et al., "The Outlook For Improved Carbon Capture Technology," Prog. Energy Combust. Sci. 38, 630 (2012).
[3] V. A. Kuuskraa, "A Program to Accelerate the Deployment of CO2 Capture and Storage (CCS): Rationale, Objectives, and Costs," Pew Center on Global Climate Change, 2007.
[4] "Electric Power Annual 2021," U.S. Energy Information Administration, November 2022, Table 4.1.
[5] G. Leo, "SNC-Lavalin-Built Carbon Capture Facility Has 'Serious Design Issues': SaskPower," CBC News, 27 Oct 15
[6] N. McQueen et al., "A Review of Direct Air Capture (DAC): Scaling Up Commercial Technologies and Innovating For the Future," Prog. Energy 3, 032001 (2021).
[7] "BP Statistical Review of World Energy," British Petroleum, June 2022.